This invention relates to microwave and waveguide circuits, and more specifically, to an improvement in a voltage controlled oscillator.
Microwave frequency voltage controlled oscillators find direct application in radar and communication systems which require the use of phase locked loops in the generation of frequency agile signals. The voltage controlled oscillator is the heart of the phase locked loop and is used to set the transmit frequencies of the system. In these systems, the ability to rapidly change frequencies is desirable. The ability of the phase locked loop to lock to a desired frequency is a direct function of the voltage controlled oscillator's frequency versus voltage characteristics, namely, the frequency linearity.
Conventional microwave frequency voltage controlled oscillators lack adequate frequency linearity. Nonlinear voltage controlled oscillator operation requires custom tailored feedback networks to compensate for nonlinear frequency performance. These feedback networks are complicated and reduce the speed at which the phase locked loop locks to a desired frequency. This in turn, causes the entire system to function at a less than optimum speed. The complexity of analog and digital linearization schemes for frequency modulated continuous wave radar applications is also related to the linearity of the master transmitter voltage controlled oscillator.
A disc resonator is commonly used in rectangular waveguides to tune RF generating solid state diodes, such as IMPATT and Gunn diodes, as oscillators. The use of a ridged waveguide to build coaxially coupled, broadband microwave oscillators is disclosed in U.S. Pat. No. 4,429,287, issued to Robertson et al. This patent shows the ridged waveguide as the circuit medium to fabricate a voltage controlled oscillator for microwave and millimeter-wave applications. A disc resonator is employed therein to tune the microwave power generating device.
It is therefore an objective of the present invention to provide an inherently linear voltage controlled oscillator, operating at microwave and millimeter-wave frequencies. A further objective of the present invention is to reduce the complexity of frequency-agile system designs.